1. Field of the Invention
The present invention relates to a recliner adjuster attached to, for example, an automobile seat for appropriately adjusting inclination of a seat back with respect to a seat cushion.
2. Description of the Related Art
A recliner adjuster is interposed between a seat cushion and a seat back that can be inclined relative to the seat cushion. A conventional recliner adjuster generally includes a guide bracket fixed to one of the seat cushion and the seat back and an internal gear fixed to the other of the seat cushion and the seat back so as to be rotatable relative to the guide bracket.
This recliner adjuster also includes a cam interposed between the guide bracket and the internal gear and coupled to a support shaft, which is concentric with a center of rotation of the internal gear relative to the guide bracket, for rotation together therewith. The cam is intended to radially slide, upon rotation of the support shaft, a lock gear interposed between the guide bracket and the internal gear and having engaging teeth formed at a distal end surface thereof. The guide bracket has a radially extending guide groove defined therein and having parallel side walls opposed to each other so that rotation of the cam may cause the lock gear to slide along the guide groove so that the engaging teeth are caused to protrude from the guide groove or withdraw inside the guide groove.
On the other hand, the internal gear has internal teeth formed along a circular arc locus having a center that is aligned with the center of rotation thereof. Rotation of the cam causes the lock gear to protrude outwardly from the guide groove to bring the engaging teeth into engagement with the internal teeth, thereby preventing rotation of the internal gear relative to the guide bracket, while reverse rotation of the cam releases the engagement between the engaging teeth and the internal teeth, thereby allowing rotation of the internal gear relative to the guide bracket.
Accordingly, by operating an operation lever to rotate the support shaft, the engaging teeth can be brought into engagement with the internal teeth to lock the seat back, while the engagement of the engaging teeth with the internal teeth can be released to change the inclination of the seat back (see, for example, Document 1).
Another recliner adjuster has been proposed having a plurality of lock gears disposed at regular intervals and a plurality of auxiliary lock gears each disposed between adjacent lock gears, wherein the lock gears slide radially upon rotation of a cam. In this recliner adjuster, if a large load is applied to the seat back due to, for example, a vehicle collision, engaging teeth of the auxiliary lock gears are brought into engagement with the internal teeth, thereby withstanding the large load (see, for example, Document 2).
Document 1: Japanese Laid-Open Patent Publication No. 2000-342370
Document 2: Japanese Laid-Open Patent Publication No. 2000-245561
In the recliner adjuster as disclosed in Document 1, if a large load applied to the seat back presses the lock gear against a side wall of the guide groove to thereby cause deformation of the side wall, the lock gear inclines and the engagement between the engaging teeth of the lock gear and the internal teeth comes loose, resulting in a reduction in the locking strength. In the case of this recliner adjuster, two lock gears are provided to ensure a sufficient locking strength when the recliner adjuster is mounted in an ordinary seat in which a large load applied to the seat back due to, for example, a vehicle collision is transmitted to a vehicle body through a seat belt. However, in the case of a belt-in-seat (seat in which a shoulder belt is incorporated) in which a large load is all applied to the recliner adjuster through the seat back, the use of a very large recliner adjuster is indispensable to withstand the large load.
On the other hand, in the recliner adjuster as disclosed in Document 2, when a large load inputted thereto exceeds a critical torque of the lock gears, the auxiliary lock gears are brought into engagement with the internal teeth so that both the lock gears and the auxiliary lock gears can withstand the large load. It is, however, not easy to stabilize the setting of the critical torque and, hence, there is still room for improvement.